function handleLogin() {
    let username =u.value;
    let password =p.value;
    $.ajax({
        url: "/check",
        data: {username, password},
        success(r) {
            if (r == -4) {
                alert("账号已经被禁用");
            } else if (r == -3) {
                alert("账号被删除");
            } else if (r == -2) {
                alert("账号和密码不匹配");
            } else if (r == -1) {
                alert("账号不存在");
            } else {
                alert("登录成功！");
                window.location.href="/";
            }
        }
    });

}